1. Field of the Invention
This invention relates generally to the radio-frequency signal mixing art and in particular to an improved balanced mixer with high conversion gain.
2. Description of the Prior Art
A mixer is a three port, time varying network which translates an RF signal at one frequency to some other intermediate frequency. To affect this translation, the RF signal is heterodyned or mixed in a non linear device with another RF signal from a local oscillator. This process generates two primary sidebands which are equal to the sum and difference between the two RF signal frequencies.
The usual method of suppressing one of the input signal components to a mixer, is to employ a balanced mixer which utilizes two nearly identical non-linear devices. However, balanced passive mixers suffer from conversion loss and must be preceded by an expensive RF amplifier. The need for an RF amplifier may be eliminated by utilizing active devices such as field effect transistors or bipolar transistors in place of the passive devices. However, in prior art active balanced mixers, substantial conversion gain is lost due to degenerative feedback effects especially whenever the received RF signal frequency is relatively close to the receivers IF frequency.